Partitioning
Two popular partition schemes are used in the wild, MBR and GPT.
MBR
MBR, or Master Boot Record, often associated with BIOS, was introduced in 1983 with IBM PC DOS 2.0, is a special boot sector located at the beginning of a drive. This sector contains a boot loader (e.g GRUB), and details about the logical partitions. MBR supports drives upto 2TiB, and up to 4 primary partitions.
# fdisk /dev/vda
Welcome to fdisk (util-linux 2.23.2).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.
Device does not contain a recognized partition table
Building a new DOS disklabel with disk identifier 0x9228f9b7.
Command (m for help): m
Command action
a toggle a bootable flag
b edit bsd disklabel
c toggle the dos compatibility flag
d delete a partition
g create a new empty GPT partition table
G create an IRIX (SGI) partition table
l list known partition types
m print this menu
n add a new partition
o create a new empty DOS partition table
p print the partition table
q quit without saving changes
s create a new empty Sun disklabel
t change a partition's system id
u change display/entry units
v verify the partition table
w write table to disk and exit
x extra functionality (experts only)
Command (m for help): n
Partition type:
p primary (0 primary, 0 extended, 4 free)
e extended
Select (default p):
Using default response p
Partition number (1-4, default 1):
First sector (2048-2097151, default 2048):
Using default value 2048
Last sector, +sectors or +size{K,M,G} (2048-2097151, default 2097151): +500M
Partition 1 of type Linux and of size 500 MiB is set
Command (m for help): l
0 Empty 24 NEC DOS 81 Minix / old Lin bf Solaris
1 FAT12 27 Hidden NTFS Win 82 Linux swap / So c1 DRDOS/sec (FAT-
2 XENIX root 39 Plan 9 83 Linux c4 DRDOS/sec (FAT-
3 XENIX usr 3c PartitionMagic 84 OS/2 hidden C: c6 DRDOS/sec (FAT-
4 FAT16 <32M 40 Venix 80286 85 Linux extended c7 Syrinx
5 Extended 41 PPC PReP Boot 86 NTFS volume set da Non-FS data
6 FAT16 42 SFS 87 NTFS volume set db CP/M / CTOS / .
7 HPFS/NTFS/exFAT 4d QNX4.x 88 Linux plaintext de Dell Utility
8 AIX 4e QNX4.x 2nd part 8e Linux LVM df BootIt
9 AIX bootable 4f QNX4.x 3rd part 93 Amoeba e1 DOS access
a OS/2 Boot Manag 50 OnTrack DM 94 Amoeba BBT e3 DOS R/O
b W95 FAT32 51 OnTrack DM6 Aux 9f BSD/OS e4 SpeedStor
c W95 FAT32 (LBA) 52 CP/M a0 IBM Thinkpad hi eb BeOS fs
e W95 FAT16 (LBA) 53 OnTrack DM6 Aux a5 FreeBSD ee GPT
f W95 Ext'd (LBA) 54 OnTrackDM6 a6 OpenBSD ef EFI (FAT-12/16/
10 OPUS 55 EZ-Drive a7 NeXTSTEP f0 Linux/PA-RISC b
11 Hidden FAT12 56 Golden Bow a8 Darwin UFS f1 SpeedStor
12 Compaq diagnost 5c Priam Edisk a9 NetBSD f4 SpeedStor
14 Hidden FAT16 <3 61 SpeedStor ab Darwin boot f2 DOS secondary
16 Hidden FAT16 63 GNU HURD or Sys af HFS / HFS+ fb VMware VMFS
17 Hidden HPFS/NTF 64 Novell Netware b7 BSDI fs fc VMware VMKCORE
18 AST SmartSleep 65 Novell Netware b8 BSDI swap fd Linux raid auto
1b Hidden W95 FAT3 70 DiskSecure Mult bb Boot Wizard hid fe LANstep
1c Hidden W95 FAT3 75 PC/IX be Solaris boot ff BBT
1e Hidden W95 FAT1 80 Old Minix
Command (m for help): t
Selected partition 1
Hex code (type L to list all codes): 83
Changed type of partition 'Linux' to 'Linux'
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.
The partition is now available as a block device, below we now see /dev/vda1:
# ls /dev/vda*
/dev/vda /dev/vda1
Let’s create a second 500G partition, on the 1GB drive /dev/vda.
# fdisk /dev/vda
Welcome to fdisk (util-linux 2.23.2).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.
Command (m for help): n
Partition type:
p primary (1 primary, 0 extended, 3 free)
e extended
Select (default p):
Using default response p
Partition number (2-4, default 2):
First sector (1026048-2097151, default 1026048):
Using default value 1026048
Last sector, +sectors or +size{K,M,G} (1026048-2097151, default 2097151): +500M
Partition 2 of type Linux and of size 500 MiB is set
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.
Done.
# ls /dev/vda*
/dev/vda /dev/vda1 /dev/vda2
Now to apply a file system. RHEL 7 by default uses xfs.
# mkfs -t xfs /dev/vda1
meta-data=/dev/vda1 isize=256 agcount=4, agsize=32000 blks
= sectsz=512 attr=2, projid32bit=1
= crc=0 finobt=0
data = bsize=4096 blocks=128000, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0 ftype=0
log =internal log bsize=4096 blocks=853, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
What file systems are currently mounted?
# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos_server1-root 9.4G 6.7G 2.7G 72% /
devtmpfs 482M 0 482M 0% /dev
tmpfs 497M 156K 497M 1% /dev/shm
tmpfs 497M 7.1M 490M 2% /run
tmpfs 497M 0 497M 0% /sys/fs/cgroup
/dev/mapper/centos_server1-home 953M 54M 899M 6% /home
/dev/vdb1 473M 156M 317M 33% /boot
tmpfs 100M 4.0K 100M 1% /run/user/42
tmpfs 100M 20K 100M 1% /run/user/1000
tmpfs 100M 0 100M 0% /run/user/0
Nothing using the new xfs /dev/vda1 partition. What block storage devices exist (regardless if actively mounted)?
# blkid
/dev/vda1: UUID="5e7ca7ad-d515-4820-b35b-ac14dffc03e4" TYPE="xfs"
/dev/vdb1: LABEL="boot" UUID="4302f187-5824-4799-980b-c816ae5b24e0" TYPE="xfs"
/dev/vdb2: UUID="OCxtoT-4gVL-DPtV-Yfdp-uMXQ-JsRE-7fjFQ4" TYPE="LVM2_member"
/dev/mapper/centos_server1-root: LABEL="root" UUID="632a6441-ba6f-4825-8a1c-c6fc14e05a9a" TYPE="xfs"
/dev/mapper/centos_server1-swap: UUID="af7fbf4b-4efc-40fc-b5de-4af06539d215" TYPE="swap"
/dev/mapper/centos_server1-home: UUID="fc985c0e-3239-47b4-bdc0-85e195f7c0fd" TYPE="xfs"
Mount /dev/vda1:
# mkdir /mnt/foomount
# mount /dev/vda1 /mnt/foomount
# cd foomount/
# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos_server1-root 9.4G 6.7G 2.7G 72% /
devtmpfs 482M 0 482M 0% /dev
tmpfs 497M 156K 497M 1% /dev/shm
tmpfs 497M 7.1M 490M 2% /run
tmpfs 497M 0 497M 0% /sys/fs/cgroup
/dev/mapper/centos_server1-home 953M 54M 899M 6% /home
/dev/vdb1 473M 156M 317M 33% /boot
tmpfs 100M 4.0K 100M 1% /run/user/42
tmpfs 100M 20K 100M 1% /run/user/1000
tmpfs 100M 0 100M 0% /run/user/0
/dev/vda1 497M 26M 472M 6% /mnt/foomount
# touch {file1,file2}
# umount /mnt/foomount/
# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos_server1-root 9.4G 6.7G 2.7G 72% /
devtmpfs 482M 0 482M 0% /dev
tmpfs 497M 156K 497M 1% /dev/shm
tmpfs 497M 7.1M 490M 2% /run
tmpfs 497M 0 497M 0% /sys/fs/cgroup
/dev/mapper/centos_server1-home 953M 54M 899M 6% /home
/dev/vdb1 473M 156M 317M 33% /boot
tmpfs 100M 4.0K 100M 1% /run/user/42
tmpfs 100M 20K 100M 1% /run/user/1000
tmpfs 100M 0 100M 0% /run/user/0
Delete a partition.
# fdisk vda
Welcome to fdisk (util-linux 2.23.2).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.
Command (m for help): p
Disk vda: 1073 MB, 1073741824 bytes, 2097152 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x9228f9b7
Device Boot Start End Blocks Id System
vda1 2048 1026047 512000 83 Linux
vda2 1026048 2050047 512000 83 Linux
Command (m for help): d
Partition number (1,2, default 2):
Partition 2 is deleted
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.
Its always good practice after modifying partition tables, to reread partition data with partprobe.
Mounting with the drive UUID, improves consistency, as dev id’s such as /dev/vda1 are not guaranteed, and is influenced by the sequence in which hardware is initialised. To mount by UUID is simple:
# blkid
/dev/vda1: UUID="5e7ca7ad-d515-4820-b35b-ac14dffc03e4" TYPE="xfs"
/dev/vdb1: LABEL="boot" UUID="4302f187-5824-4799-980b-c816ae5b24e0" TYPE="xfs"
/dev/vdb2: UUID="OCxtoT-4gVL-DPtV-Yfdp-uMXQ-JsRE-7fjFQ4" TYPE="LVM2_member"
/dev/mapper/centos_server1-root: LABEL="root" UUID="632a6441-ba6f-4825-8a1c-c6fc14e05a9a" TYPE="xfs"
/dev/mapper/centos_server1-swap: UUID="af7fbf4b-4efc-40fc-b5de-4af06539d215" TYPE="swap"
/dev/mapper/centos_server1-home: UUID="fc985c0e-3239-47b4-bdc0-85e195f7c0fd" TYPE="xfs"
# mount -U 5e7ca7ad-d515-4820-b35b-ac14dffc03e4 /mnt/foomount
# ls /mnt/foomount
file1 file2
GPT
GPT, or GUID Partition Table, often associated with UEFI, assigns a unique identifier (GUID) to each partition. GPT overcomes many of MBT’s limitationsm, and offers some nice resiliance features, such as storing multiple copies of the boot and partitioning data across the drive, and storing CRC for detecting possible data integrity issues. Thanks to its 64 bit addressing can support disk sizes up to 8ZiB and 128 primary partitions.
# gdisk /dev/vda
GPT fdisk (gdisk) version 0.8.6
Command (? for help): n
Partition number (1-128, default 1):
First sector (34-2097118, default = 2048) or {+-}size{KMGTP}:
Last sector (2048-2097118, default = 2097118) or {+-}size{KMGTP}: +500M
Current type is 'Linux filesystem'
Hex code or GUID (L to show codes, Enter = 8300):
Changed type of partition to 'Linux filesystem'
Command (? for help): w
Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!
Do you want to proceed? (Y/N): Y
OK; writing new GUID partition table (GPT) to /dev/vda.
The operation has completed successfully.
The new partition is now a device (i.e. available in /dev):
# ls /dev/vda*
/dev/vda /dev/vda1
Apply a file system to the partition.
# mkfs -t xfs -f /dev/vda1
meta-data=/dev/vda1 isize=256 agcount=4, agsize=32000 blks
= sectsz=512 attr=2, projid32bit=1
= crc=0 finobt=0
data = bsize=4096 blocks=128000, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0 ftype=0
log =internal log bsize=4096 blocks=853, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
Mount it:
# mount /dev/vda1 -t xfs /sillymount
Once mounted df will report it:
# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos_server1-root 9.4G 6.7G 2.7G 72% /
/dev/vdb1 473M 156M 317M 33% /boot
/dev/mapper/centos_server1-home 953M 54M 899M 6% /home
/dev/vda1 497M 26M 472M 6% /mnt/sillymount
It’s better to use the UUID of the partition to mount it:
Unmount:
# umount sillymount
List device UUID’s:
# blkid
/dev/vdb1: LABEL="boot" UUID="4302f187-5824-4799-980b-c816ae5b24e0" TYPE="xfs"
/dev/vdb2: UUID="OCxtoT-4gVL-DPtV-Yfdp-uMXQ-JsRE-7fjFQ4" TYPE="LVM2_member"
/dev/mapper/centos_server1-root: LABEL="root" UUID="632a6441-ba6f-4825-8a1c-c6fc14e05a9a" TYPE="xfs"
/dev/mapper/centos_server1-swap: UUID="af7fbf4b-4efc-40fc-b5de-4af06539d215" TYPE="swap"
/dev/mapper/centos_server1-home: UUID="fc985c0e-3239-47b4-bdc0-85e195f7c0fd" TYPE="xfs"
/dev/vda1: UUID="6d2da03c-eea0-4630-b19b-c067ca790cf1" TYPE="xfs" PARTLABEL="Linux filesystem" PARTUUID="2f6035f7-d4c0-4f06-becb-6cd2afc7ceed"
Mount using UUID with -U switch:
# mount -U 6d2da03c-eea0-4630-b19b-c067ca790cf1 -t xfs /mnt/sillymount
Logical Volume Management
Attach Block Devices
To experiment with LVM (logical volume manager), using a KVM machine, attach a few 1GB storage devices.
virsh # vol-list default
Name Path
------------------------------------------------------------------------------
server1.example.com.qcow2 /var/lib/libvirt/images/server1.example.com.qcow2
silly-volume-1.qcow2 /var/lib/libvirt/images/silly-volume-1.qcow2
silly-volume-2.qcow2 /var/lib/libvirt/images/silly-volume-2.qcow2
silly-volume-3.qcow2 /var/lib/libvirt/images/silly-volume-3.qcow2
virsh # domblklist server1.example.com
Target Source
------------------------------------------------
vda /var/lib/libvirt/images/server1.example.com.qcow2
vdb /var/lib/libvirt/images/silly-volume-1.qcow2
vdc /var/lib/libvirt/images/silly-volume-2.qcow2
vdd /var/lib/libvirt/images/silly-volume-3.qcow2
hda -
Partitions
For each block device, we need to add a (GPT) partition of type Linux LVM. Rinse and repeat with gdisk, for example, given block device /dev/vdd:
# gdisk vdd
GPT fdisk (gdisk) version 0.8.6
Partition table scan:
MBR: not present
BSD: not present
APM: not present
GPT: not present
Creating new GPT entries.
Command (? for help): n
Partition number (1-128, default 1):
First sector (34-2097118, default = 2048) or {+-}size{KMGTP}:
Last sector (2048-2097118, default = 2097118) or {+-}size{KMGTP}:
Current type is 'Linux filesystem'
Hex code or GUID (L to show codes, Enter = 8300): 8e00
Changed type of partition to 'Linux LVM'
Command (? for help): w
Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!
Do you want to proceed? (Y/N): Y
OK; writing new GUID partition table (GPT) to vdd.
The operation has completed successfully.
Physical Volume
Register the desired partitions as LVM physical volumes, using pvcreate.
# pvcreate /dev/vdc1 /dev/vdd1
Physical volume "/dev/vdc1" successfully created
Physical volume "/dev/vdd1" successfully created
And, confirm physical volume creation with pvdisplay:
# pvdisplay
--- Physical volume ---
PV Name /dev/vdb2
VG Name centos_server1
PV Size 11.21 GiB / not usable 4.00 MiB
Allocatable yes
PE Size 4.00 MiB
Total PE 2870
Free PE 3
Allocated PE 2867
PV UUID OCxtoT-4gVL-DPtV-Yfdp-uMXQ-JsRE-7fjFQ4
"/dev/vdc1" is a new physical volume of "1022.98 MiB"
--- NEW Physical volume ---
PV Name /dev/vdc1
VG Name
PV Size 1022.98 MiB
Allocatable NO
PE Size 0
Total PE 0
Free PE 0
Allocated PE 0
PV UUID U3tvfK-0Bfe-Gc6a-EHUU-YlAr-FV99-ZdO8Hc
"/dev/vdd1" is a new physical volume of "1022.98 MiB"
--- NEW Physical volume ---
PV Name /dev/vdd1
VG Name
PV Size 1022.98 MiB
Allocatable NO
PE Size 0
Total PE 0
Free PE 0
Allocated PE 0
PV UUID 4sR7Qv-G58b-b6HG-N2rZ-SjSu-fGS3-nPIr10
Volume Group
Enlist previously registered physical volumes into what is known as a volume group. Note vgcreate takes an alias (cylon in the example).
vgcreate cylon /dev/vdc1 /dev/vdd1
Volume group “cylon” successfully created
Confirming desired result with vgdisplay:
vgdisplay
— Volume group —
VG Name cylon
System ID
Format lvm2
Metadata Areas 2
Metadata Sequence No 1
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 0
Open LV 0
Max PV 0
Cur PV 2
Act PV 2
VG Size 1.99 GiB
PE Size 4.00 MiB
Total PE 510
Alloc PE / Size 0 / 0
Free PE / Size 510 / 1.99 GiB
VG UUID iC4m8Z-7c4K-n1H4-MVB4-RaIY-nV9q-zYdJ6S
Logical Volumes
Finally, we can create the logical volumes that will manifest themselves as block devices to operating system, which in turn can have file systems applied to them and so on. Lets create two logical volumes, a 1GB called “starbuck”, and a 500M called “boomer”:
# lvcreate -n starbuck -L 1G cylon
Logical volume "starbuck" created.
# lvcreate -n boomer -L 500M cylon
Logical volume "boomer" created.
Verify logical volumes with lvdisplay:
# lvdisplay
--- Logical volume ---
LV Path /dev/cylon/starbuck
LV Name starbuck
VG Name cylon
LV UUID UlhcnB-HuPX-OXDV-IL1U-uCGv-Hnfs-fFkGIs
LV Write Access read/write
LV Creation host, time server1.example.com, 2017-07-08 08:44:32 -0400
LV Status available
# open 0
LV Size 1.00 GiB
Current LE 256
Segments 2
Allocation inherit
Read ahead sectors auto
- currently set to 8192
Block device 253:3
--- Logical volume ---
LV Path /dev/cylon/boomer
LV Name boomer
VG Name cylon
LV UUID qik2FG-cM1F-JXY7-yoaW-U5ve-qfjM-iO6bwK
LV Write Access read/write
LV Creation host, time server1.example.com, 2017-07-08 08:47:32 -0400
LV Status available
# open 0
LV Size 500.00 MiB
Current LE 125
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 8192
Block device 253:4
You can see both are sitting on the volume group named cylon. Speaking of cylon, how much capacity does it have?
# vgdisplay
--- Volume group ---
VG Name cylon
System ID
Format lvm2
Metadata Areas 2
Metadata Sequence No 3
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 2
Open LV 0
Max PV 0
Cur PV 2
Act PV 2
VG Size 1.99 GiB
PE Size 4.00 MiB
Total PE 510
Alloc PE / Size 381 / 1.49 GiB
Free PE / Size 129 / 516.00 MiB
VG UUID iC4m8Z-7c4K-n1H4-MVB4-RaIY-nV9q-zYdJ6S
Can see its got 516 MiB free, nice.
Apply File System
LVM logical volumes get mapped into the /dev tree under their volume group name, i.e. /dev/vg-name/lv-name, for example:
# cd /dev/cylon
# ls
boomer starbuck
They can be treated as a normal block device.
# mkfs -t xfs boomer
meta-data=boomer isize=256 agcount=4, agsize=32000 blks
= sectsz=512 attr=2, projid32bit=1
= crc=0 finobt=0
data = bsize=4096 blocks=128000, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0 ftype=0
log =internal log bsize=4096 blocks=853, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
Mount the freshly minted xfs LVM logical volume:
# mkdir /mnt/boomer && mount /dev/cylon/boomer /mnt/boomer
# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos_server1-root 9.4G 6.7G 2.7G 72% /
/dev/mapper/cylon-boomer 497M 26M 472M 6% /mnt/boomer
Removal of LVM artefacts
Lets teardown everything in reverse order, starting with logical volumes:
# lvremove /dev/cylon/boomer
Do you really want to remove active logical volume boomer? [y/n]: y
Logical volume "boomer" successfully removed
# lvremove /dev/cylon/starbuck
Do you really want to remove active logical volume starbuck? [y/n]: y
Logical volume "starbuck" successfully removed
Then the volume group:
# vgremove cylon
Volume group "cylon" successfully removed
Finally the physical volumes:
# pvremove /dev/vdc1
Labels on physical volume "/dev/vdc1" successfully wiped
# pvremove /dev/vdd1
Labels on physical volume "/dev/vdd1" successfully wiped
Extending Logical Volumes
Growing LVM volumes just works.
vgextend cylon /dev/vda4
lgextend -L +20G /dev/cylon/toaster
Increasing the recognised storage increase to active mounts, it a matter of getting the specific file system involved, in this XFS:
xfs_growfs /mnt/toaster
Mount File Systems at Boot
For the demonstration, lets apply two different flavours of file system to a couple of block devices, xfs and ext4.
First ensure block devices have been partitioned, example:
# gdisk /dev/vdd
GPT fdisk (gdisk) version 0.8.6
Command (? for help): n
Partition number (1-128, default 1):
First sector (34-2097118, default = 2048) or {+-}size{KMGTP}:
Last sector (2048-2097118, default = 2097118) or {+-}size{KMGTP}:
Current type is 'Linux filesystem'
Hex code or GUID (L to show codes, Enter = 8300):
Changed type of partition to 'Linux filesystem'
Command (? for help): w
Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!
Do you want to proceed? (Y/N): Y
OK; writing new GUID partition table (GPT) to /dev/vdd.
The operation has completed successfully.
Make one of the partitions xfs:
mkfs -t xfs -f /dev/vdd
And the other ext4:
mkfs -t ext4 /dev/vdc
Lets verify the situation with blkid:
# blkid
/dev/vdb1: LABEL="boot" UUID="4302f187-5824-4799-980b-c816ae5b24e0" TYPE="xfs"
/dev/vdc: UUID="1b7fe6d4-66f6-4fda-b971-489be9c68b36" TYPE="ext4"
/dev/vdd: UUID="86c6cfe6-4cf4-4bb6-bec1-13a72d588896" TYPE="xfs"
Labelling File Systems
XFS
Labelling is a file system specific capability. For example for xfs based systems, to write a label:
# xfs_admin -L master-chief /dev/vdd
writing all SBs
new label = "master-chief"
To read label:
# xfs_admin -l /dev/vdd
label = "master-chief"
Ext4
For Ext4, to write a label:
# tune2fs -L cortana /dev/vdc
tune2fs 1.42.9 (28-Dec-2013)
To read label:
# tune2fs -l /dev/vdc
tune2fs 1.42.9 (28-Dec-2013)
Filesystem volume name: cortana
Finally blkid will attempt to query labels too:
$blkid
/dev/vdc: LABEL="cortana" UUID="1b7fe6d4-66f6-4fda-b971-489be9c68b36" TYPE="ext4"
/dev/vdd: LABEL="master-chief" UUID="86c6cfe6-4cf4-4bb6-bec1-13a72d588896" TYPE="xfs"
Auto Mounting
The file /etc/fstab contains descriptive information about the filesystems the system can mount. Each filesystem is described on a separate line. Fields on each line are separated by tabs or spaces. Lines starting with ‘#’ are comments. Blank lines are ignored.
The following is a typical example of an fstab entry:
LABEL=t-home2 /home ext4 defaults,auto_da_alloc 0 2
Checkout fstab(5) and mount(8). The fourth field defaults sets the following options:
rwread-writesuidallow suid or sgid bits to take effectdevinterpret character or block special devices on the filesystemexecpermit execution of binariesautocan be mounted with the -a optionnouserforbid an ordinary (non-root) user to mount the filesystemasyncall I/O should be done asynchonously
There are lots of other interesting options, such as:
(lazytime) Only update times (atime, mtime, ctime) on the in-memory version of the file inode. This mount option significantly reduces writes to the inode table for workloads that perform frequent random writes to preallocated files.
The fifth field is known as the dump field, to flag which filesystems need to be dumped.
The sixth field, the check disk field, is used by fsch(8), to determine the order in which filesystem checks are done at boot time. The root FS should be 1 and others to 2. Default is to not check (0).
First up register the XFS block device /dev/vdd by its UUID. To find the UUID use blkid:
# blkid
/dev/vdb1: LABEL="boot" UUID="4302f187-5824-4799-980b-c816ae5b24e0" TYPE="xfs"
/dev/vdb2: UUID="OCxtoT-4gVL-DPtV-Yfdp-uMXQ-JsRE-7fjFQ4" TYPE="LVM2_member"
/dev/vdc: LABEL="cortana" UUID="1b7fe6d4-66f6-4fda-b971-489be9c68b36" TYPE="ext4"
/dev/vdd: LABEL="master-chief" UUID="86c6cfe6-4cf4-4bb6-bec1-13a72d588896" TYPE="xfs"
We can see /dev/vdd UUID. Time to edit the /etc/fstab, by adding the following:
UUID=86c6cfe6-4cf4-4bb6-bec1-13a72d588896 /mnt/master-chief xfs defaults 0 0
Save, and ask mount to reparse fstab (using the -a switch) to take care of any new devices.
# mount -a
# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos_server1-root 9.4G 6.7G 2.7G 72% /
/dev/vdd 1014M 33M 982M 4% /mnt/master-chief
vdd is now mounted at /mnt/master-chief. Boom!
Finally, let mount the Ext4 block device /dev/vdc by its label cortana:
# blkid
/dev/vdc: LABEL="cortana" UUID="1b7fe6d4-66f6-4fda-b971-489be9c68b36" TYPE="ext4"
Edit /etc/fstab again, adding the following:
LABEL=cortana /mnt/cortana ext4 defaults 0 0
Refresh:
# mount -a
# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos_server1-root 9.4G 6.7G 2.7G 72% /
/dev/vdd 1014M 33M 982M 4% /mnt/master-chief
/dev/vdc 976M 2.6M 907M 1% /mnt/cortana
Swap space
Swap space, or virtual memory, is fake memory the kernel provides when memory pressure is experienced, by buffering the most stale parts of memory out to swap disk (a block device). free shows current memory utilisation including swap.
# free -m
total used free shared buff/cache available
Mem: 992 462 121 8 408 361
Swap: 975 0 975
Some other useful ways to get current swap details:
# swapon -s
Filename Type Size Used Priority
/dev/dm-1 partition 999420 0 -1
/dev/vda1 partition 1047528 0 -2
Or:
# cat /proc/swaps
Filename Type Size Used Priority
/dev/dm-1 partition 999420 0 -1
/dev/vda1 partition 1047528 0 -2
One common rule of thumb for swap sizing, is double the amount of memory.
Method 1 LVM
Chuck an LVM partition on your block device. I’m using /dev/vda, a 1GB block device I just attached to my VM.
# gdisk /dev/vda
GPT fdisk (gdisk) version 0.8.6
Command (? for help): n
Partition number (1-128, default 1):
First sector (34-2097118, default = 2048) or {+-}size{KMGTP}:
Last sector (2048-2097118, default = 2097118) or {+-}size{KMGTP}:
Current type is 'Linux filesystem'
Hex code or GUID (L to show codes, Enter = 8300): 8e00
Command (? for help): w
Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!
Do you want to proceed? (Y/N): Y
OK; writing new GUID partition table (GPT) to /dev/vda.
The operation has completed successfully.
Now the LVM tango, create a physical volume (PV), a volume group (VG) and logical volume (LV).
# pvcreate /dev/vda1
Physical volume "/dev/vda1" successfully created
# vgcreate quake /dev/vda1
Volume group "quake" successfully created
# lvcreate -n quake-swap -L 500M quake
Logical volume "quake-swap" created.
/dev/quake/quake-swap has been born! Format it as swap:
# mkswap /dev/quake/quake-swap
Setting up swapspace version 1, size = 511996 KiB
no label, UUID=af9378e2-3e60-4c3e-ba8c-1ae9a885b0a1
Before automounting it, verify it works by sparking it up with swapon:
# swapon /dev/quake/quake-swap
# free -m
total used free shared buff/cache available
Mem: 992 481 98 8 413 342
Swap: 1475 0 1475
Notice swap just increased 500MB.
# swapoff /dev/quake/quake-swap
Auto mount with /etc/fstab, by adding a similar entry. This could be device based, label based or UUID based, as demonstrated earlier.
/dev/quake/quake-swap swap swap defaults 0 0
To refresh auto mounting swap:
# swapon -a
Method 2 Block device
Partition the block device, this time as a Linux swap partition.
# gdisk /dev/vda
GPT fdisk (gdisk) version 0.8.6
Command (? for help): n
Partition number (1-128, default 1):
First sector (34-2097118, default = 2048) or {+-}size{KMGTP}:
Last sector (2048-2097118, default = 2097118) or {+-}size{KMGTP}:
Current type is 'Linux filesystem'
Hex code or GUID (L to show codes, Enter = 8300): 8200
Changed type of partition to 'Linux swap'
Command (? for help): w
Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!
Do you want to proceed? (Y/N): Y
OK; writing new GUID partition table (GPT) to /dev/vda.
The operation has completed successfully.
Format time:
# mkswap /dev/vda1
Setting up swapspace version 1, size = 1047528 KiB
no label, UUID=d5fb1252-f823-43ac-a8ea-bdd641e397b9
Test it:
# swapon /dev/vda1
# free -m
total used free shared buff/cache available
Mem: 992 501 92 8 398 309
Swap: 1998 0 1998
Register it to automount. First locate the UUID of the block device:
# blkid
....
/dev/vda1: UUID="d5fb1252-f823-43ac-a8ea-bdd641e397b9" TYPE="swap" PARTLABEL="Linux swap" PARTUUID="1dfffa52-1454-493f-95ce-e84671ae161c"
And register it in /etc/fstab:
UUID=d5fb1252-f823-43ac-a8ea-bdd641e397b9 swap swap defaults 0 0
And do a full swap refresh:
# swapoff -a
# swapon -a
# swapon -s
Filename Type Size Used Priority
/dev/dm-1 partition 999420 0 -1
/dev/vda1 partition 1047528 0 -2
umount -a will unmount everything in fstab.
File Systems (VFAT, EXT4 and XFS)
VFAT
As an evolution to the earlier FAT (File Allocation Table), provides support for longer file names. It is backwards compatible with FAT, and is arguably the most ubiquitous file systems on the planet, supported by most operating systems, making it a good fit for interoperability between computers. To apply vfat to a block device:
# mkfs.vfat /dev/vda1
mkfs.fat 3.0.20 (12 Jun 2013)
Temporary mount:
# mount /dev/vda1 /mnt/vfat
# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos_server1-root 9.4G 6.7G 2.7G 72% /
/dev/vda1 1021M 4.0K 1021M 1% /mnt/vfat
Persistent mount (/etc/fstab):
/dev/vda1 /mnt/vfat vfat defaults 0 0
To run a filesystem check (must be unmounted):
fsck.vfat /dev/vda1
EXT4
Born in 2008 the fourth extended file system bought a number of performance and enhancements (such as greater storaeg limits) to predecessor ext3. The ext family of filesystems are commonly managed using the e2fsprogs utilities. Some examples.
To create a new ext4 filesystem:
# mkfs.ext4 /dev/vdb1
mke2fs 1.42.9 (28-Dec-2013)
Filesystem label=
...
To run an integrity (must be unmounted):
fsck /dev/vdb1
dumpe2fs is useful for gathering information:
# dumpe2fs /dev/vda2
dumpe2fs 1.42.9 (28-Dec-2013)
Filesystem volume name: <none>
Last mounted on: <not available>
Filesystem UUID: 10487788-2839-47be-a8fe-03573fba245c
Filesystem magic number: 0xEF53
Filesystem revision #: 1 (dynamic)
Filesystem features: has_journal ext_attr resize_inode dir_index filetype extent 64bit flex_bg sparse_super large_ file huge_file uninit_bg dir_nlink extra_isize
Filesystem flags: signed_directory_hash
Default mount options: user_xattr acl
Filesystem state: clean
Errors behavior: Continue
Filesystem OS type: Linux
Inode count: 65536
Block count: 261883
Reserved block count: 13094
Free blocks: 253024
Free inodes: 65525
First block: 0
Block size: 4096
Fragment size: 4096
Group descriptor size: 64
Reserved GDT blocks: 127
Blocks per group: 32768
Fragments per group: 32768
Inodes per group: 8192
Inode blocks per group: 512
Flex block group size: 16
Filesystem created: Sun Nov 12 05:48:52 2017
Last mount time: n/a
Last write time: Sun Nov 12 05:48:52 2017
Mount count: 0
Maximum mount count: -1
Last checked: Sun Nov 12 05:48:52 2017
Check interval: 0 (<none>)
Lifetime writes: 17 MB
Reserved blocks uid: 0 (user root)
Reserved blocks gid: 0 (group root)
First inode: 11
Inode size: 256
Required extra isize: 28
Desired extra isize: 28
Journal inode: 8
Default directory hash: half_md4
Directory Hash Seed: 8126fa63-b9e0-43e3-81d9-d8d7eb0c1986
Journal backup: inode blocks
Journal features: (none)
Journal size: 16M
Journal length: 4096
Journal sequence: 0x00000001
Journal start: 0
Group 0: (Blocks 0-32767)
Checksum 0xaa72, unused inodes 8181
Primary superblock at 0, Group descriptors at 1-1
Reserved GDT blocks at 2-128
Block bitmap at 129 (+129), Inode bitmap at 145 (+145)
Inode table at 161-672 (+161)
28521 free blocks, 8181 free inodes, 2 directories, 8181 unused inodes
Free blocks: 142-144, 153-160, 4258-32767
Free inodes: 12-8192
Group 1: (Blocks 32768-65535) [INODE_UNINIT]
Checksum 0x4d1e, unused inodes 8192
Backup superblock at 32768, Group descriptors at 32769-32769
Reserved GDT blocks at 32770-32896
Block bitmap at 130 (bg #0 + 130), Inode bitmap at 146 (bg #0 + 146)
Inode table at 673-1184 (bg #0 + 673)
32639 free blocks, 8192 free inodes, 0 directories, 8192 unused inodes
Free blocks: 32897-65535
Free inodes: 8193-16384
Group 2: (Blocks 65536-98303) [INODE_UNINIT]
Checksum 0x71c7, unused inodes 8192
Block bitmap at 131 (bg #0 + 131), Inode bitmap at 147 (bg #0 + 147)
Inode table at 1185-1696 (bg #0 + 1185)
28672 free blocks, 8192 free inodes, 0 directories, 8192 unused inodes
Free blocks: 69632-98303
Free inodes: 16385-24576
...
tune2fs allows us to modify parameters, here we apply a label:
# tune2fs -L darthvader /dev/vda2
tune2fs 1.42.9 (28-Dec-2013)
XFS
Born back in 1993 by Silicon Graphics, is a high performance (thanks to its parallel I/O design based on allocation groups) 64-bit journaling file system. It was ported to the Linux kernel in 2001. To create a new XFS filesystem:
# mkfs.xfs -f /dev/vda1
meta-data=/dev/vda1 isize=256 agcount=4, agsize=65471 blks
= sectsz=512 attr=2, projid32bit=1
= crc=0 finobt=0
data = bsize=4096 blocks=261883, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0 ftype=0
log =internal log bsize=4096 blocks=853, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
Unlike ext4 which leans on the excellent e2fsprogs utils, XFS has its own variations of these which include: xfs_admin, xfs_bmap, xfs_copy, xfs_db, xfs_estimate, xfs_freeze, xfs_fsr, xfs_growfs, xfs_info, xfs_io, xfs_logprint, xfs_mdrestore, xfs_metadump, xfs_mkfile, xfs_ncheck, xfs_quota, xfs_repair, xfs_rtcp, xfsdump, xfsinvutil, xfsrestore
xfs_info for example provides information about a specific XFS filesystem:
# xfs_info /dev/vda1
meta-data=/dev/vda1 isize=256 agcount=4, agsize=65471 blks
= sectsz=512 attr=2, projid32bit=1
= crc=0 finobt=0
data = bsize=4096 blocks=261883, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0 ftype=0
log =internal bsize=4096 blocks=853, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
To apply a label:
# xfs_admin -L obiwan /dev/vda1
xfs_admin: /dev/vda1 contains a mounted filesystem
fatal error -- couldn't initialize XFS library
Oops, XFS must be unmounted in order to label it:
# umount /mnt/xfs
# xfs_admin -L obiwan /dev/vda1
writing all SBs
new label = "obiwan"
To run an XFS integrity check (must be unmounted):
# xfs_repair /dev/vda1
Phase 1 - find and verify superblock...
Phase 2 - using internal log
- zero log...
- scan filesystem freespace and inode maps...
- found root inode chunk
Phase 3 - for each AG...
- scan and clear agi unlinked lists...
- process known inodes and perform inode discovery...
- agno = 0
- agno = 1
- agno = 2
- agno = 3
- process newly discovered inodes...
Phase 4 - check for duplicate blocks...
- setting up duplicate extent list...
- check for inodes claiming duplicate blocks...
- agno = 0
- agno = 1
- agno = 2
- agno = 3
Phase 5 - rebuild AG headers and trees...
- reset superblock...
Phase 6 - check inode connectivity...
- resetting contents of realtime bitmap and summary inodes
- traversing filesystem ...
- traversal finished ...
- moving disconnected inodes to lost+found ...
Phase 7 - verify and correct link counts...
done